Kelly Clancy is a neuroscientist studying the biology of intelligence. She has held research positions at MIT, Berkeley, University College London, and the AI company DeepMind. Her essays have appeared in Wired, Harper’s, and The New Yorker.

Below, Clancy shares five key insights from her new book, Playing with Reality: How Games Have Shaped Our World. Listen to the audio version—read by Clancy herself—in the Next Big Idea App.

1. Play is an instinct.

Games are an extraordinary invention. A game—whether a video game, board game, casino game, or otherwise—is an arrangement of ideas the brain devised to give itself free pleasure out of nothing. In other words, the brain created games to hack itself.

We’ve had some sense of this for thousands of years: the Greek historian Herodotus wrote about the Lydian people who supposedly invented many of the games we play today. He claims the Lydians went through 18 years of famine. They’d alternate between eating one day and playing games the next to lessen their hunger. In many ways, games nourish us.

Play is ancient. Games speak to something deep in us, beyond time, culture, and language. Humans have played games like chess, go, and backgammon for thousands of years. Play is much older than humans, in fact. Many animals and even insects play. Animals play to practice physical skills—like kittens pouncing on toys to practice hunting.

Humans, on the other hand, play games to practice mental skills. Play is learning. Through play, our brains set up a safe environment to acquire new experiences. We’ve learned a lot about the world and about learning by studying games. Even if you don’t play games as an adult, the games you played as a child set up a lot of how you think and experience the world today. Games are not an invention. They’re an instinct.

2. The power of probability.

Games can help us make better choices. For thousands of years, people have used cards, dice, and lots to make unbiased decisions. In Biblical times, the Israelites used lots to divide inheritances and draft military conscripts fairly. Historically, religious leaders were the only people allowed to interpret dice throws to make decisions and settle disputes. The word clergy comes from the Greek word kleros, meaning “lot or chance.” But more fundamentally, playing games can teach us how to plan and strategize better.

Mathematicians have more recently formalized the relationship between games and decision-making. Gambling was hugely popular in Renaissance Europe, and players studied dice to improve their win rate. This eventually led to the invention of probability theory. For the first time, we had a mathematical language to rigorously express what we don’t know rather than what we do know. Probability theory fueled the scientific revolution because it helped scientists analyze actual data and express uncertainties in their measurements. Whereas people once chalked up every event to the whims of the gods, probability theory enabled us to make quantified forecasts about the future. Today, it seems mundane to say something like, “There’s a 40 percent chance of rain tomorrow.” But this is a revolutionary capability. We can make data-informed decisions thanks to games.

This mathematical revolution touched nearly every academic discipline and birthed several new fields. German military strategists used statistics to turn the game of chess into Kriegsspiel, a war simulation game used to workshop battles. War—once considered an art—became a science, and Kriegsspiel helped the Germans reshape the face of Europe in the late nineteenth century. When Charles Darwin was preparing his radical work on evolution, he was frustrated that he didn’t know enough math to express his ideas more concretely. Sixty years later, biologists would discover that the same mathematics used to describe dice rolls would capture the flow of natural selection. Many concepts foundational to modern economics, science, and medicine—like odds, incentives, and expected value—come from games.

3. People aren’t selfish.

In a 1944 book, John von Neumann and Oskar Morgenstern introduced a new branch of mathematics known as game theory. They wanted to answer one question: How do you optimally play a game if you don’t know how your opponent will act? Game theory was von Neumann’s attempt to understand the forces shaping human behavior. Von Neumann, a Hungarian Jew, fled Europe in 1933 just as Hitler came into power. He was deeply disturbed by the Nazis and hoped to work out a theory for truly rational behavior during a deeply irrational time. He and Morgenstern modeled the world as a game, with human players within that game. This framework allowed them to ask: How does a player make choices that maximize their odds of winning?

4. Games play us.

Game theory forms the basis of modern economics. It’s also a fundamentally incorrect model of people. This is more than a theoretical problem. If we build systems based on the assumption that people are selfish, we can doom them to act that way. The celebrated board game designer Reiner Knizia says the first thing he does when designing a new game is to develop a scoring system. The way the game rewards players dictates how they act. Take Monopoly, for instance. To win, a player must act like a greedy capitalist. Even if the player is a socialist in real life, they have to play the game that’s there, not the game they wish it were. They can’t win by profit sharing or refusing to take rent. This is insidious. Today, games are hidden everywhere in our technologies. Game design dictates how we interact on social media, how dating apps match us, how companies serve ads, and more. We’re moving in hidden games and being rewarded for behaviors we may not be proud of—in other words, games play us.

Games are like casts of the mind. Each game is purpose fit to different mental functions. This also makes them a bit dangerous—throughout history, people have known games can be addictive. Ancient Hindu rajas compare dice to a drug. In Renaissance Venice (where casinos were born), gambling nearly deposed the ruling class as the aristocracy gambled their family fortunes away. Today, companies gamify their products to enthrall us to their platforms. Gamified work apps push employees to work harder and longer than is safe. We need to be more aware of who is creating the games we move in and whether our values align with those of the game designers.

5. Thinking like a game designer.

Some of the greatest thinkers in history have promised that games can teach us important life lessons. Plato believed that children’s games were critical civic education because they taught future citizens how to follow rules. In Medieval times, knights and the nobility were required to learn chess. Playing chess was thought to be like looking into a mirror because you could learn about yourself by playing it. Today, many business leaders play games like poker to learn how to read people. The statesman Henry Kissinger claimed that to understand Chinese leaders, Western policymakers should learn to play Go. And games can teach us how to be better negotiators and strategists. But we can also take a step back and ask an even more fundamental question—not just how do we play games better, but are we playing the games we want to be playing? And how do we build better games?

For example, you can think about how you run a business in terms of game design. A surprising number of the biggest names in tech got their start making games. One of Bill Gates’ earliest programs played tic-tac-toe. Young Sundar Pichai, now CEO of Google, developed a chess engine. Salesforce’s Marc Benioff sold games like Crypt of the Undead to Atari. You can get really good at thinking at the systems level by studying how games work and how to design particular dynamics. This field is called mechanism design, and economists use it to design new marketplaces, voting systems, and more. They hope to build fairer games where everyone wins.

This article originally appeared in Next Big Idea Club magazine and is reprinted with permission.